As one of optical communication technologies, there is a technology of measuring dense wavelength-multiplexed optical signals. For example, there has been proposed a technology of measuring the total electrical field amplitude of wavelength-multiplexed optical signals multiple times at predetermined time intervals, and calculating electrical field amplitudes of signal components with different wavelengths by performing Fourier analysis on the measurement results.
In addition, there is a technology of measuring the light power of each sub-channel signal in a super-channel system. For example, there has been proposed a technology of detecting light power of a sub-channel signal (transmission optical signal) by: performing low-speed frequency modulation on the sub-channel signal of which the light power is to be detected; and measuring the transmitted light power while sweeping a wavelength variable filter on the modulated sub-channel signal.
Related techniques are disclosed in, for example, International Publication Pamphlet No. WO 2009/145070 and Japanese Laid-open Patent Publication No. 2013-201495.